Pneumonia: Causes, symptoms and management

What Is Pneumonia?


Pneumonia is an infection that affects one or both lungs. It causes the air sacs, or alveoli, of the lungs to fill up with fluid or pus. Bacteria, viruses, or fungi may cause pneumonia. Symptoms can range from mild to serious and may include a cough with or without mucus (a slimy substance), fever, chills, and trouble breathing. How serious your pneumonia is depends on your age, your overall health, and what caused your infection.

To diagnose pneumonia, your healthcare provider will review your medical history, perform a physical exam, and order diagnostic tests such as a chest X-ray. This information can help determine what type of pneumonia you have.

Treatment for pneumonia may include antibiotic, viral, or fungal medicines. It may take several weeks to recover from pneumonia. If your symptoms get worse, you should see a healthcare provider right away. If you have severe pneumonia, you may need to go to the hospital for antibiotics given through an intravenous (IV) line and oxygen therapy.

Causes of pneumonia


Bacteria are a common cause of pneumonia in adults. Many types of bacteria can cause pneumonia, but Streptococcus pneumoniae (also called pneumococcus bacteria) is the most common cause in the United States. 

Some bacteria cause pneumonia with different symptoms or other characteristics than the usual pneumonia. This infection is called atypical pneumonia. For example, Mycoplasma pneumoniae causes a mild form of pneumonia often called “walking pneumonia.” Legionella pneumophila causes a severe type of pneumonia called Legionnaires’ disease. Bacterial pneumonia can develop on its own or after you have a cold or the flu.


Viruses that infect your lungs and airways can cause pneumonia. The flu (influenza virus) and the common cold (rhinovirus) are the most common causes of viral pneumonia in adults. Respiratory syncytial virus (RSV) is the most common cause of viral pneumonia in young children.


Many other viruses can cause pneumonia, including SARS-CoV-2, the virus that causes COVID-19.


Fungi such as Pneumocystis jirovecii may cause pneumonia, especially for people who have weakened immune systems. Some fungi found in the soil in the southwestern United States and in the Ohio and Mississippi River valleys can also cause pneumonia.


The symptoms of pneumonia can be mild or serious. Young children, older adults, and people who have serious health conditions are at risk for developing more serious pneumonia or life-threatening complications.

The symptoms of pneumonia may include:

  • Chest pain when you breathe or cough
  • Chills
  • Cough with or without mucus
  • Fever
  • Low oxygen levels in your blood, measured with a pulse oximeter
  • Shortness of breath

You may also have other symptoms, including a headache, muscle pain, extreme tiredness, nausea (feeling sick to your stomach), vomiting, and diarrhea.

Older adults and people who have serious illnesses or weakened immune systems may not have the typical symptoms. They may have a lower-than-normal temperature instead of a fever. Older adults who have pneumonia may feel weak or suddenly confused.

Sometimes babies don’t have typical symptoms either. They may vomit, have a fever, cough, or appear restless or tired and without energy. Babies may also show the following signs of breathing problems: 

  • Bluish tone to the skin and lips
  • Grunting
  • Pulling inward of the muscles between the ribs when breathing
  • Rapid breathing
  • Widening of the nostrils with each breath

Diagnostic tests and procedures

If your provider thinks you have pneumonia, he or she may do one or more of the following tests.

  • A chest X-ray looks for inflammation in your lungs. A chest X-ray is often used to diagnose pneumonia.
  • Blood tests, such as a complete blood count (CBC) see whether your immune system is fighting an infection.
  • Pulse oximetry measures how much oxygen is in your blood. Pneumonia can keep your lungs from getting enough oxygen into your blood. To measure the levels, a small sensor called a pulse oximeter is attached to your finger or ear.

If you are in the hospital, have serious symptoms, are older, or have other health problems, your provider may do other tests to diagnose pneumonia.

  • A blood gas test may be done if you are very sick. For this test, your provider measures your blood oxygen levels using a blood sample from an artery, usually in your wrist. This is called an arterial blood gas test.
  • A sputum test, using a sample of sputum (spit) or mucus from your cough, may be used to find out what germ is causing your pneumonia.
  • A blood culture test can identify the germ causing your pneumonia and also show whether a bacterial infection has spread to your blood.
  • A polymerase chain reaction (PCR) test quickly checks your blood or sputum sample to find the DNA of germs that cause pneumonia.
  • A bronchoscopy looks inside your airways. If your treatment is not working well, this procedure may be needed. At the same time, your doctor may also collect samples of your lung tissue and fluid from your lungs to help find the cause of your pneumonia.
  • A chest computed tomography (CT) scan can show how much of your lungs are affected by pneumonia. It can also show whether you have complications such as lung abscesses or pleural disorders. A CT scan shows more detail than a chest X-ray.
  • A pleural fluid culture can be taken using a procedure called thoracentesis, which is when a doctor uses a needle to take a sample of fluid from the pleural space between your lungs and chest wall. The fluid is then tested for bacteria.



Your healthcare provider may prescribe some of the following medicines to treat your pneumonia at home or at the hospital, depending on how sick you are.

Management at home

If your pneumonia is mild, your provider may prescribe medicines or suggest over-the-counter medicines to treat it at home.

  • Antibiotics may be prescribed for bacterial pneumonia. Most people begin to feel better after one to three days of antibiotic treatment. However, you should take antibiotics as your doctor prescribes. If you stop too soon, your pneumonia may come back.
  • Antiviral medicine is sometimes prescribed for viral pneumonia. However, these medicines do not work against every virus that causes pneumonia.
  • Antifungal medicines are prescribed for fungal pneumonia.
  • Over-the-counter medicines may be recommended to treat your fever and muscle pain or help you breathe easier. Talk to your provider before taking cough or cold medicine.

Management at the hospital

If your pneumonia is serious, you may be treated in a hospital so you can get antibiotics and fluids through an intravenous (IV) line inserted into your vein. You may also get oxygen therapy to increase the amount of oxygen in your blood. If your pneumonia is very serious, you may need to be put on a ventilator.


You may need a procedure or surgery to remove seriously infected or damaged parts of your lung. This may help you recover and may prevent your pneumonia from coming back.



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